Gear Ratios

Putting a new motor and gears in a K's Johnson 0-4-0T. Its tiny, about length of tender so need tiny motor. But was wondering gear ratios. Now in
simple terms if its an Express with big wheels then use 38:1 Slow freight eg 4F with heavy load, 20mm wheels then 50:1 Express freight eg cauliflower with modest load, 20mm wheels 38:1
But what would the team recommend for Johnson 0-4-0 T with its expected slow speed, just few wagons, wheels 15mm ?
Suggestions wellcome and corrections to basic assumptions.
Cheers, Simon
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simon wrote:

I'd be looking at higher ratios. Similar sized locos are available in kit form from High Level, they come with 100:1 (or thereabouts) gearboxes. High Level kits are very good, run superbly; I have built quite a few.
High Level's gearboxes are available as components; try one with a small Mashima motor.
http://www.highlevelkits.co.uk /
- Nigel
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simon wrote:

I'd agree with Nigel 100% - I would use something like 80:1 or 100:1 using one of High Level Kits gearboxes. There isn't a model that one of these won't fit one way or another, and there's a PDF you can download showing the various gearboxes actual size for planning. I use these almost exclusively.
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I know, I know, thats how should do it. Tis just that had enough of learning curve without doing more. Will ponder.....Did read last night that these engines were rated to pull 35 empty wagons or 25 full at Burton shed so maybe you are right.
Cheers, Simon
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simon wrote:

Well, if you're on a learning curve than High Level Kit's gearboxes are ideal because they go together nicely without lots of faffing about trying to mesh gears. About the only "specialist" tool you'll need is a broach to ease out the bearing and idler shaft holes to be a snug fit - and that's true of any quality etch.
Taking Greg's point, yes, if you do want occasional bursts of speed then 60:1 might be better. It's really up to you! If you do go for an HLK gearbox, then the worm stage can be changed at a later stage if you change your mind about the ratio. Incidentally, HLK's gearboxes use multiple stage reduction gearing so there are no high reduction worm and pinion gears so setting up is easy.
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Must admit was a bit concerned about the speed cos of small wheels. Had made that mistake with Cauliflower by putting a 60:1 gear and it didnt half whirr when trying to go express freight speed. Just so happens that cauliflower has a small diameter motor with that 60:1, so have removed them and put it into the Johnson tank. Had to do a bit of fettling but its in and the enclosed motor will look excellent as bottom half of boiler when painted black. Swapped pickups from (steel ?) wire to phosphor bronze and its now a nice little runner. Will see what its pulling power is when add couplings. Doubt if ran on mainline very often as some of them only carried 400 galls of water and no coal bunker.
Thanks for advice Simon
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The K's motor was fairly low reving whereas any modern small motor will run to impossible revs. (say double the K's) If you want the 0-4-0T to occasionally run on the mainline then 80:1-100:1 will be too great a reduction because the loco will take forever. The other downside of high reduction ratios is the noise (you might not care, of course) The high revs will wear the motor bearings much quicker than a lower reduction. High reduction worm and pinion gears are much finer than the common ratios and so require much more careful setting up.
If you can change the gear ratio later I would suggest trying 60:1.
One system I've made use of is putting a large pinion (spur gear) on the driven axle and a small pinion or spur gear on the gearbox axle so that a lowish reduction ratio is multiplied 2 - 2.5 - 3 times. I have to admit I first did this because I only had a Tri-ang worm/pinion in my parts box and nothing suitable could be bought in NZ. The gearbox axle mounted gear can sit anywhere around the driven axle gear so it gives a better choice of motor location.
It's apparently common to use a spur gear reduction before the gearbox, but I reject that as being too buzzy with the spur gears running much faster than after the worm-drive gearbox.
Regards, Greg.P.
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